/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.util;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FilenameFilter;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * 
 * @since solr 1.3
 */
public class VersionedFile {
	/*
	 * Open the latest version of a file... fileName if that exists, or the last
	 * fileName.* after being sorted lexicographically. Older versions of the
	 * file are deleted (and queued for deletion if that fails).
	 */
	public static InputStream getLatestFile(String dirName, String fileName)
			throws FileNotFoundException {
		Collection<File> oldFiles = null;
		final String prefix = fileName + '.';
		File f = new File(dirName, fileName);
		InputStream is = null;

		// there can be a race between checking for a file and opening it...
		// the user may have just put a new version in and deleted an old
		// version.
		// try multiple times in a row.
		for (int retry = 0; retry < 10 && is == null; retry++) {
			try {
				if (!f.exists()) {
					File dir = new File(dirName);
					String[] names = dir.list(new FilenameFilter() {
						public boolean accept(File dir, String name) {
							return name.startsWith(prefix);
						}
					});
					Arrays.sort(names);
					f = new File(dir, names[names.length - 1]);
					oldFiles = new ArrayList<File>();
					for (int i = 0; i < names.length - 1; i++) {
						oldFiles.add(new File(dir, names[i]));
					}
				}

				is = new FileInputStream(f);
			} catch (Exception e) {
				// swallow exception for now
			}
		}

		// allow exception to be thrown from the final try.
		if (is == null) {
			is = new FileInputStream(f);
		}

		// delete old files only after we have successfuly opened the newest
		if (oldFiles != null) {
			delete(oldFiles);
		}

		return is;
	}

	private static final Set<File> deleteList = new HashSet<File>();

	private static synchronized void delete(Collection<File> files) {
		synchronized (deleteList) {
			deleteList.addAll(files);
			List<File> deleted = new ArrayList<File>();
			for (File df : deleteList) {
				try {
					df.delete();
					// deleteList.remove(df);
					deleted.add(df);
				} catch (SecurityException e) {
					if (!df.exists()) {
						deleted.add(df);
					}
				}
			}
			deleteList.removeAll(deleted);
		}
	}
}
